ARTICLE

A Self-Powered Breath Analyzer Based on PANI/PVDFPiezo-Gas-Sensing Arrays for Potential Diagnostics Application

Yongming Fu1,2 . Haoxuan He3 . Tianming Zhao3 . Yitong Dai3 . Wuxiao Han3 . Jie Ma2 . Lili Xing1,3 .

Yan Zhang1 . Xinyu Xue1,3

Received: 30 July 2018 / Accepted: 21 October 2018 / Published online: 12 November 2018

� The Author(s) 2018

Highlights

• A self-powered breath analyzer based on polyaniline/polyvinylidene fluoride (PANI/PVDF) piezo-gas-sensing arrays

was developed for a potential diagnostics application.

• The device works by converting energy from exhaled breath into electrical sensing signals without any external power

sources.

• The working principle can be attributed to the coupling of in-pipe gas-flow-induced piezoelectric effect of PVDF

bellows and gas-sensing effect of PANI electrodes.

Abstract The increasing morbidity of internal diseases

poses serious threats to human health and quality of life.

Exhaled breath analysis is a noninvasive and convenient

diagnostic method to improve the cure rate of patients. In

this study, a self-powered breath analyzer based on

polyaniline/polyvinylidene fluoride (PANI/PVDF) piezo-

gas-sensing arrays has been developed for potential

detection of several internal diseases. The device works by

converting exhaled breath energy into piezoelectric gas-

sensing signals without any external power sources. The

five sensing units in the device have different sensitivities

to various gas markers with concentrations ranging from 0

to 600 ppm. The working principle can be attributed to the

coupling of the in-pipe gas-flow-induced piezoelectric

effect of PVDF and gas-sensing properties of PANI elec-

trodes. In addition, the device demonstrates its use as an

ethanol analyzer to roughly mimic fatty liver diagnosis.

This new approach can be applied to fabricating new

exhaled breath analyzers and promoting the development

of self-powered systems.

110.070.0060.0050.0040.0030.0020.0010.00

100

80

60

40

20

0

Res

pons

e (%

)

PANI(NA)PANI(CA)

PANI(SO)PANI(SDS)

PANI(SS)

acetone

carbon monoxide

ethanol

oxynitride

methane

110.070.0060.0050.0040.0030.0020.0010.00

100

80

60

40

20

0

Res

pons

e (%

)

PANI(NA)PANI(CA)

PANI(SO)PANI(SDS)

PANI(SS)

acetone

carbon monoxide

ethanol

oxynitride

methane

PAPANI(PANoxide

thanolide

Electronic supplementary material The online version of thisarticle (https://doi.org/10.1007/s40820-018-0228-y) contains supple-mentary material, which is available to authorized users.

& Lili Xing

xinglili@mail.neu.edu.cn

& Yan Zhang

zhangyan@uestc.edu.cn

& Xinyu Xue

xuexinyu@mail.neu.edu.cn

1 School of Physics, University of Electronic Science and

Technology of China, Chengdu 610054, People’s Republic of

China2 College of Physics and Electronics Engineering, Shanxi

University, Taiyuan 030006, People’s Republic of China

3 College of Sciences, Northeastern University,

Shenyang 110004, People’s Republic of China

123

Nano-Micro Lett. (2018) 10:76(0123456789().,-volV)(0123456789().,-volV)

https://doi.org/10.1007/s40820-018-0228-y

Keywords Polyaniline � Polyvinylidene fluoride �Piezoelectric � Sensor array � Diagnostics � Breath analyzer

1 Introduction

In recent years the increasing morbidity of internal diseases

induced by unwholesome diet and working behaviors has

posed a serious threat to human health and quality of life

[1–3]. Early detection and treatment play key roles in

improving the cure rate of the patients [4]. Although con-

ventional blood examination methods have been developed

with good sensitivity and stability [5], a noninvasive,

portable, and convenient diagnostic method is urgently

needed for a wide range of early diagnoses and high-risk

population screening [6]. As an important physiological

process for human beings, breath is one of the most

important ways to exchange substances between the human

body and outside world. Various studies suggest that

exhaled breath, containing a large number of metabolic

products, includes gas species and concentrations closely

associated with human health as indicators of certain dis-

eases [7–12]. For example, ethanol in exhaled breath is

recognized as a gas marker of fatty liver; oxynitride (NOx)

is a gas marker of airway inflammation; acetone is a gas

marker of diabetes; methane (CH4) is a gas marker of liver

cirrhosis; and carbon monoxide (CO) is a gas marker of

asthma. However, exhaled breath analyzers are restricted

by possible limitations, such as high cost, structure com-

plexity, need for high-quality materials, and reliance on

external power sources.

Self-powered systems aimed at powering portable and

wearable electronics with human motion have been

developed based on piezoelectric or triboelectric nano-

generators [13–19]. In addition, conducting polymer-based

gas sensors are widely used in room-temperature detection

of exhaled gas markers [20–23]. Compared with tribo-

electric nanogenerators [24, 25], piezoelectric nanogener-

ators can work without the contact–separation process

between two materials, which is more suitable for con-

structing portable self-powered devices. By simultaneously

carrying out power generation and gas sensing, the inte-

gration of the piezoelectric nanogenerator and gas sensor in

a single device may be a feasible way to realize a self-

powered exhaled breath analyzer. A novel and distinct

device architecture should be developed adapting to the

convenience and compatibility of exhaled breath analysis.

In this paper, we report a self-powered breath analyzer

based on polyaniline/polyvinylidene fluoride (PANI/

PVDF) piezo-gas-sensing arrays for a potential diagnostics

application. PANI is an easily synthesized conducting

polymer that is widely used in room-temperature gas-

sensing applications [23]. PVDF is a piezoelectric polymer

with a high piezoelectric coefficient and flexibility [26].

Based on coupling of the in-pipe gas-flow-induced piezo-

electric effect of PVDF and gas-sensing properties of PANI

electrodes, the exhaled breath analyzer can convert energy

from exhaled breath into piezoelectric gas-sensing signals.

The device consists of five different sensing units, with

each sensing unit having favorable selectivity to a partic-

ular gas marker. The sensing signals of every sensing unit

hold a proportional relationship with gas concentration in a

wide range (from 0 to 600 ppm), along with outstanding

room-temperature response/recovery kinetics. This work

launches a new working principle in the exhaled breath

detection field and greatly advances the applicability of

self-powered systems.

2 Experimental Procedures

2.1 Fabrication of PANI Electrodes

First, a piece of copper foil (5 cm 9 5 cm 9 10 lm) was

covered with a photoresist pattern by photolithography.

Then, the copper foil was wet-etched by soaking with

aqueous sodium persulfate (0.5 mol L-1) at 50 �C for

2 min, followed by immersion into developer for 30 s to

remove the residual photoresist. Second, PANI derivatives

were deposited on Cu substrate by electrochemical poly-

merization. The growing solution contained equal molar

concentrations (0.2 mol L-1) of dopant and aniline

monomer. Sodium sulfate, sodium dodecylbenzene sul-

fonate, sodium oxalate, camphorsulfonic acid, and nitric

acid were used as dopant sources in each of the five PANI

derivatives. The Pt wafer, Ag/AgCl electrode, and Pt wire

served as the working, reference, and counter electrodes,

respectively. The electrochemical reaction was employed

at 1.2 V with 0.05 V s-1 for 200 s to polymerize PANI.

Finally, twist pattern PANI electrodes were obtained by

etching in aqueous sodium persulfate (0.5 mol L-1) at

50 �C for 2 min to remove the copper substrate.

2.2 Device Fabrication

PVDF gel was obtained by adding 1 g of PVDF powder

into 10 mL of acetone and stirring at 60 �C for 30 min.

Then, the PVDF gel was spin-coated on PANI electrodes at

200 rpm for 30 s and dried at room temperature for 2 h to

form PVDF/PANI film. To enhance the piezoelectricity of

PVDF, the film was polarized under an electric field of

20 kV mm-1 at 80 �C for 30 min. A 100-nm Cu film was

deposited on the back of PVDF by electron beam

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76 Page 2 of 12 Nano-Micro Lett. (2018) 10:76

evaporation. Finally, PANI/PVDF bellows was obtained by

extrusion molding at 60 �C for 24 h in a 3D-printed model.

2.3 Characterization and Measurements

For accurate measurement, five PANI electrodes were

separately glued to a copper wire as working electrodes,

and a copper wire was glued to the back of the Cu film as a

shared counter electrode. During the test, the device was

placed at one end of a gas pipe connected to a gas cylinder

and air compressor. The rate and concentration of gas flow

were controlled by gas flowmeters. The gas-sensing per-

formances were studied by measuring the output current in

the circuit under different conditions. The gas flow rate was

held at 8 m s-1 unless specified otherwise. The output

current was measured by a low-noise current preamplifier

(SR570, Stanford Research Systems) and collected by a

data acquisition card (PCI-1712, Advantech) in the com-

puter. The morphology and composition of PANI deriva-

tives were investigated by a scanning electron microscope

(SEM; Hitachi S4800) with an energy-dispersive spec-

trometer (EDS).

3 Results and Discussion

Figure 1a is a schematic diagram of the proposed working

mechanism of a self-powered exhaled breath analyzer. As a

human subject blows into the analyzer, the current signal

generated by PANI/PVDF piezoelectric bellows can be

measured through a current amplifier and displayed on a

computer. Amplitude of the current signal is related to the

gases detected in exhaled breath, such that the character-

istic of exhaled breath is deduced by calculating the vari-

ation of measured signals. The photograph of un-rolled

PANI/PVDF film and PANI/PVDF bellows is shown in

Fig. 1b. The basic structure of the device mainly consists

of three functional parts: Twist PANI patterns function as

both working electrodes and gas-sensing material; PVDF

film works as the power source through the in-pipe gas-

flow-induced piezoelectric effect; and Cu film on the back

works as the shared counter electrode. As the bellows

configuration was widely used in mechanical energy con-

version by extending/retracting along the radial direction

[27, 28], the PVDF film is formed into bellows to pro-

ductively enhance the efficiency of converting breath

energy into piezoelectricity. In the as-fabricated device, the

thickness of PVDF and PANI is uniform and the 100-nm

Cu film is deposited on the whole back surface of PVDF as

the shared counter electrode. There are five individual

PANI electrodes in one as-fabricated device, and each

electrode can be separately connected with an external

circuit for electrical measurements, as shown in Fig. S1.

The twist pattern structure of PANI electrodes is employed

to improve the lifetime and stability as the bellows vibrates

with high frequency under blowing. The detailed fabrica-

tion progress of the device is shown in Fig. 1c. In brief, a

piece of Cu foil is etched to a twist pattern by pho-

tolithography; five PANI derivatives are separately

deposited on twisted Cu electrodes by electrochemical

polymerization; PANI/PVDF film is obtained by spin-

coating the PVDF gel on PANI electrodes; PANI/PVDF

bellows is shaped up from PANI/PVDF film through

extrusion forming. Figure 1d shows a typical SEM image

of selected region in one sensing unit (nitric acid-doped

PANI), demonstrating that the width of PANI electrode is

* 2 mm. Figure 1e is a SEM image of the PANI/PVDF

interface enlarged from Fig. 1d, showing that the height of

PANI is lower than that of PVDF. Figure 1f is a SEM

image of the PVDF film, demonstrating that the PVDF

surface is smooth, and no pores or fractures can be

observed.

To propose the working principle, a lumped parameter

equivalent circuit model of the self-powered exhaled breath

analyzer can be derived from three circuit elements in a

circuit (Fig. 1g) [29–33]: The first one is the voltage term,

which originates from the generated piezoelectric polar

dipoles in PVDF and can be represented by an ideal voltage

source (V); the second one is a capacitance term, which

originates from the inherent capacitance of PVDF between

the two electrodes and can be represented by a capacitor

(C); the third one is a resistance term, which originates

from the variation of PANI derivatives influenced by the

atmosphere and can be represented by a resistance (R). The

capacitor and voltage source of PVDF are parallel-con-

nected to each other and series-connected with the resis-

tance of PANI. Figure 1h shows the generated output

current in a few cycles, confirming that the output current

is an AC electrical signal.

One can observe that there are five twist PANI elec-

trodes in a single device, and each PANI derivative is

doped with different dopant sources. The sensing units are

labeled as PANI(SS), PANI(SDS), PANI(SO), PANI(CA),

and PANI(NA) with respect to the dopants (sodium sulfate,

sodium dodecylbenzene sulfonate, sodium oxalate, cam-

phorsulfonic acid, and nitric acid, respectively). Figure 2a–

e shows the SEM images of PANI(SS), PANI(SDS),

PANI(SO), PANI(CA), and PANI(NA), respectively,

demonstrating the distinctness of the surface morphology

of each sample. Figure 2f shows the EDS spectra of the

five PANI derivatives. C, N, and O elements can be clearly

found in the five samples, while the S element can only be

found in PANI(SS), PANI(SDS), and PANI(CA) samples.

The absence of the Na element verifies that acid group

anions are grafted with PANI chains as a dopant source

during the polymerization process [23]. Figure 2g shows

123

Nano-Micro Lett. (2018) 10:76 Page 3 of 12 76

Raman spectra of the five PANI derivatives. As observed,

the peaks around 1580 cm-1 can be assigned to the C=C

stretching vibrations of quinoid ring; the peaks around

1500 cm-1 can be assigned to the C=C stretching vibra-

tions of benzene ring; and the band around 1350 cm-1

provides the information on C*N?� vibrations of delo-

calized polaronic structures [34]. These results indicate that

diverse PANI derivatives are successfully synthesized

through electrochemical polymerization and that molecular

conformation of PANI can be affected by changing

dopants. I–V curves of the five PANI derivatives are shown

in Fig. S2, indicating that the conductivity is significantly

influenced by the dopant through charge redistribution in

PANI chains [35, 36]. Figure 2h illustrates the XRD

PhotolithographyElectrochemicalpolymerization

Rolling

(a)

(c)

Cu PANI

Extrusion molding Etching substrate

Depositing electrode

PVDF Molds Spin-coatingPVDF

(b)

)e()d(

PVDF

PVDFPVDF

PANIPANI

1 mm 10 µm

5 µm

PVDF(f) )h()g(

R

A

C

AmperemeterPVDF

PANIV

604020

0− 20− 40− 60

0 10 20 30Time (ms)

40 50

Cur

rent

(nA

)

Fig. 1 Structure and fabrication of the device. a Proposed concept. b Photographs of un-rolled PANI/PVDF film and as-fabricated bellows.

c Fabrication process of the device. d SEM image of PANI/PVDF. e High-magnification SEM image of PANI/PVDF interface. f SEM image of

PVDF film. g Lumped parameter equivalent circuit model of the device. h A few cycles of the output current

123

76 Page 4 of 12 Nano-Micro Lett. (2018) 10:76

pattern of the PVDF film. The dominating peak around

20.72� is narrow and strong, which belongs to (110) and

(200) of beta-phase PVDF [37]. Figure 2i is the FTIR

spectrum of the PVDF film. The typical peaks around 1400

and 840 cm-1 can be indexed to stretching of beta-phase

PVDF; the peaks around 1070 and 760 cm-1 can be

indexed to stretching of alpha-phase PVDF; and the peak

around 880 cm-1 can be indexed to stretching of amor-

phous-phase PVDF [38]. These results indicate that the

polarized PVDF film is a mixed phase with beta-phase is

predominant phase, making the fabricated PVDF an

effective piezoelectric film.

Figure 3 shows the sensing performance of one

PANI(SS) sensing unit in different ambient atmospheres

with gas concentrations ranging from 0 to 600 ppm. The

gas flow rate is held constant at 8 m s-1. Figure S3 shows

the continuous output current of the PANI(SS) sensing unit

under an airflow rate of 8 m s-1 for 12 h, exhibiting a

slight decrease in the output current after long-time service

(the mechanical fatigue of PVDF). Figure 3a–e illustrates

that the output current significantly decreases with an

increasing concentration of acetone, CO, ethanol, and CH4

with discernible differences, but in turn increases with

increasing NOx concentration. Video S1 shows the real-

time sensing process of the PANI(SS) unit against 600 ppm

ethanol gas flow. To calculate the relationship between

output current and gas concentration, the gas response (Rg)

of the device can be simply defined as [39–41]:

Rg% ¼Ia � Ig��

��

Ia� 100%; ð1Þ

where Ia and Ig represent the output current of the device in

air and the output current with a particular concentration of

gas marker, respectively. The response curves with respect

to acetone, CO, ethanol, CH4, and NOx are shown in

Fig. 3f. With the gas concentration ranging from 100 to

600 ppm in steps of 100 ppm, the response to acetone is

11.0%, 15.1%, 25.7%, 41.8%, 57.0%, and 68.2%; the

response to CO is 6.4%, 11.6%, 16.7%, 22.1%, 28.5%, and

30.3%; the response to ethanol is 11.9%, 15.6%, 21.3%,

24.5%, 29.2%, and 31.6%; the response to NOx is 1.1%,

3.3%, 7.1%, 10.6%, 12.7%, and 15.8%; and the response to

CH4 is 5.7%, 8.9%, 12.2%, 17.1%, 23.2%, and 26.4%,

respectively. As a maximum, the response to 600 ppm

PANI(SS)PANI(SDS)PANI(SO)PANI(CA)PANI(NA)

PANI(SS)PANI(SDS)PANI(SO)PANI(CA)PANI(NA)

CN O S

Cou

nts

0 1 2 3 4Energy (kV)

10099989796959493

Tran

smitt

ance

(%)

4000 3000Wavenumber (cm−1)

2000 10002000 1500Wavenumber (cm−1)

1000 500

100

50

0

Inte

nsity

(a.u

.)

Inte

nsity

(a.u

.)

10 20 30 40 50 602θ (degree)

5 µm

)e()d(

)c()b()a(

(f)

(i)(h)(g)

5 µm

)OS(INAP)SDS(INAP)SS(INAP

)AN(INAP)AC(INAP

5 µm 5 µm

5 µm

Fig. 2 Characterization of the PANI/PVDF. a–e SEM images of PANI(SS), PANI(SDS), PANI(SO), PANI(CA), and PANI(NA), respectively.

f EDS spectra of the five PANI derivatives. g Raman spectra of the five PANI derivatives. h XRD pattern of PVDF film. i FTIR spectrum of

PVDF film

123

Nano-Micro Lett. (2018) 10:76 Page 5 of 12 76

acetone is 68.2%, indicating that the PANI(SS) sensing unit

has a promising selectivity against acetone. It can be

observed that the gas response is not linear, which may be

induced by the nonlinear resistance variation of PANI.

Similar nonlinear response curves are often observed in

other resistive-type gas sensors, such as metal oxide-based

sensors and conducting polymer-based sensors [42, 43].

It has been reported that PANI derivatives doped with

diverse dopants demonstrate different selectivities toward

various gas markers [23]. The sensing performance of

sensing units with different PANI derivatives in their par-

ticular gas atmospheres is shown in Fig. 4. With a con-

centration from 0 to 600 ppm of particular gas markers, the

output current of PANI(SDS) in response to ethanol

(Fig. 4a) is 42.7, 38.4, 35.0, 30.1, 24.2, 20.8, and 18.4 nA;

the output current of PANI(SO) in response to CO (Fig. 4b)

is 47.1, 42.0, 38.1, 34.9, 30.5, 27.4, and 24.9 nA; the output

current of PANI(CA) in response to NOx (Fig. 4c) is 51.0,

60.2, 73.9, 78.7, 85.4, 95.7, and 104.6 nA; and the output

current of PANI(NA) in response to CH4 (Fig. 4d) is 62.0,

52.8, 46.2, 42.7, 38.9, 35.9, and 28.8 nA, respectively.

Figure 4e shows the relationship of the four sensing units

between the output current and the concentration of gas

markers. The response of the five sensing units to 600 ppm

of particular gas markers is shown in Fig. 4f, with the gas

marker of PANI(SS), PANI(SDS), PANI(SO), PANI(CA),

and PANI(NA) as acetone, ethanol, CO, NOx, and CH4,

respectively. The maximum response of each sensing unit

to 600 ppm of gas marker is 68.2%, 56.9%, 47.1%,

105.1%, and 53.5%, respectively. Similar results are found

in several previous studies, which can be attributed to the

dopant-induced change of morphology and conformation

of PANI derivatives [44, 45]. These results indicate the

potential application of the device as a self-powered

exhaled breath analyzer for disease diagnostics.

Figure 5 shows the real-time continuously measured

current profiles of the five sensing units to illustrate the

dynamic response/recovery process with particular gas

markers, all of which exhibit a slow response and a fast

recovery time. The response time of PANI(SS),

PANI(SDS), PANI(SO), PANI(CA), and PANI(NA) is

* 50, 63, 67, 54, and 52 s, while the recovery time is

* 15, 24, 18, 40, and 28 s, respectively. Such relatively

slow response/recovery process is common in room-tem-

perature gas sensors [46, 47]. The recovery process is faster

than the response time, which may be ascribed to the high-

speed gas flow measurement conditions for desorption of

gas molecules from PANI film. This proves that the

approach is an effective method for real-time exhaled

breath detection.

The piezoelectric output current of PANI/PVDF bellows

is affected by gas flow rate. Therefore, the influence of the

gas flow rate is investigated, and the results are shown in

Figs. S4 and 6. Figure S4 shows that the frequency of

output current increases under airflow rate in the range of

1–10 m s-1. Figure 6a shows the output current of the

PANI(SS) unit with increasing airflow rate. The sensing

unit outputs a tiny current with airflow rates lower than

3 m s-1, while the output current significantly increases

with airflow rates over 3 m s-1. Under low gas flow rates,

vibrations are mainly induced by turbulent buffeting, while

under high gas flow rates, they are mainly induced by

elastic excitation. The vibrations rapidly increase with tiny

increments in the gas flow rate when the gas flow rate is

60

30

0

− 30

− 60

Cur

rent

(nA

)

0 200 100 200

(a)

300400 500

600

40 60 80Time (s)

acetone concentration (ppm)60

30

0

− 30

− 60

Cur

rent

(nA

)

0 20

0 100 200

(b)

300 400 500 600

40 60 80Time (s)

CO concentration (ppm)

60

30

0

− 30

− 60

Cur

rent

(nA

)

0 200 100 200

(d)

300 400 500 600

40 60 80Time (s)

CH4 concentration (ppm)60

30

0

− 30

− 60C

urre

nt (n

A)

0 20

0 100 200

)f()e(

300 400 500 600

40 60 80 100 200 300 400 500Concentration (ppm)

600

70605040302010

0

Time (s)

NOx concentration (ppm)

60

30

0

− 30

− 60

Cur

rent

(nA

)

0 200 100 200

(c)

300 400 500 600

40 60 80Time (s)

ethanol concentration (ppm)

acetoneCOethanolCH4NOx

Res

pons

e (%

)

Fig. 3 Performances of PANI(SS) sensing unit. a–e The output current of PANI(SS) in response to acetone, CO, ethanol, CH4, and NOx with

concentrations ranging from 0 to 600 ppm. f The relationship between the response and gas concentration

123

76 Page 6 of 12 Nano-Micro Lett. (2018) 10:76

just over a certain threshold [48]. With an airflow rate

ranging from 4 to 9 m s-1, the output current is 27.6, 33.2,

36.3, 41.0, 47.2, 53.7, and 55.9 nA, respectively, showing a

linearly increasing trend. The output current reaches satu-

ration with airflow rates over 9 m s-1. Figure 6b, c shows

the output current of the five sensing units with air and with

600 ppm of gas markers, respectively, indicating that the

output current of every sensing unit linearly increases both

in airflow and gas markers with the gas flow rate ranging

from 4 to 9 m s-1. Interestingly, the calculated responses

are almost maintained at a constant level, as shown in

Fig. 6d. The result shows that the gas flow rate has a

negligible effect on gas response, further supporting the

possibility of the device utilization in self-powered exhaled

breath analysis.

For breath analysis applications, humidity dependence

on gas response of the device is very important. Figure 7

shows the influence of humidity on the ethanol response of

the PANI(SDS) sensing unit. The relative humidity (RH)

was controlled as 40%, 60%, 80%, and 100% RH,

respectively. The output current of the PANI(SDS) sensing

unit under airflow and 600 ppm ethanol gas flow in dif-

ferent humidity conditions is shown in Fig. 7a. From

Fig. 7b, it can be observed that the output current increases

with increasing RH in airflow, but decreases with

increasing RH in ethanol gas flow. When the device is in

60

30

0

− 30

− 60

Cur

rent

(nA

)

0 20

0 0100

)b()a(

)d()c(

)f()e(

100200 200

0 100 200 300 400 500 600200 300 400 500 600

1000

300 300400 400500 500

600 600

40 60 80Time (s)

60

30

0

− 30

− 60

Cur

rent

(nA

)

0 20 40 60 80Time (s)

120

60

0

− 60

− 120

Cur

rent

(nA

)

0 20 40 60 80Time (s)

60

30

0

− 30

− 60C

urre

nt (n

A)

0 20 40 60 80Time (s)

)mpp( noitartnecnoc OC-)OS(INAP)mpp( noitartnecnoc lonahte-)SDS(INAP

PANI(CA)-NOx HC-)AN(INAP)mpp( noitartnecnoc 4 concentration (ppm)

110.070.0060.0050.0040.0030.0020.0010.00

100

80

60

40

20

100

80

60

40

20

0

Cur

rent

(nA

)

0200

400600

Concentration (ppm)

ethanol

oxynitride

methanecarbon monoxide

Res

pons

e (%

)

PANI(NA)PANI(CA)

PANI(SO)PANI(SDS)

PANI(SS)

acetone

carbon monoxide

ethanol

oxynitride

methane

PAPANI(PANoxide

thanolride

PANI(SDS)PANI(SO)PANI(CA)PANI(NA)

Fig. 4 Sensing performances of the five sensing units. The output current of a PANI(SDS) unit under different ethanol concentrations.

b PANI(SO) unit under different CO concentrations. c PANI(CA) unit under different NOx concentrations. d PANI(NA) unit under different CH4

concentrations. e The relationship of the four units between the output current and special gas marker concentration. f The response of the five

sensing units to 600 ppm gases

123

Nano-Micro Lett. (2018) 10:76 Page 7 of 12 76

100

50

0

− 50

− 100

Cur

rent

(nA

)

0 20 40 60 80 100 120Time (s)

100

50

0

− 50

− 100

Cur

rent

(nA

)

0 20 40 60 80 100 120Time (s)

150100

500

− 50− 100

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rent

(nA

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0 20 40 60 80 100 120Time (s)

100

50

0

− 50

− 100

Cur

rent

(nA

)

0 20 40 60 80 100 120Time (s)

In air In 600 ppm gas

6030

0− 30− 60

Cur

rent

(nA

)

0 20 40 60 80 100 120Time (s)

PANI(NA) for CH4

PANI(CA) for NOxPANI(SO) for CO

PANI(SDS) for ethanolPANI(SS) for acetone)b()a(

)d()c(

(e)

Fig. 5 Response/recovery processes of the sensing units. a PANI(SS) for acetone. b PANI(SDS) for ethanol. c PANI(SO) for CO. d PANI(CA)

for NOx. e PANI(NA) for CH4

75

50

25

0

− 25

− 50

− 75

Cur

rent

(nA

)

0 30

(c) (d)

(b)(a)

0 1 2 34 5 6 7 8

9 10 11 12

60 90Time (s)

120 150

Gasflow rate (m s−1)

PANI(SS)PANI(SDS)PANI(SO)PANI(CA)PANI(NA)

80

70

60

50

40

30

20

Cur

rent

(nA

)

4 5 6Gasflow rate (m s−1)

7 8 9

PANI(SS)PANI(SDS)PANI(SO)

120

100

80

60

40

20

0

120

100

80

60

40

20

0

Res

pons

e (%

)

4 5 6Gasflow rate (m s−1)

7 8 9

PANI(SS)PANI(SDS)PANI(SO)PANI(CA)PANI(NA)

Cur

rent

(nA

)

4 5 6Gasflow rate (m s−1)

7 8 9

PANI(CA)PANI(NA)

Fig. 6 Sensing performances of the five units under different gas flow rates. a The output current of PANI(SS) unit under airflow rates in the

range of 0–12 m s-1. b The output current of five sensing units under airflow rates in the range of 4–9 m s-1. c The output current of five sensingunits in response to 600 ppm special gas marker under gas flow rate in the range of 4–9 m s-1. d The relationship of the five sensing units

between responses and gas flow rates

123

76 Page 8 of 12 Nano-Micro Lett. (2018) 10:76

humid airflow, water molecules can infiltrate pores in the

PANI film to enhance conductivity and increase the output

current. When the device is in humid ethanol gas flow,

ethanol molecules react with PANI chains to decrease the

doping level of PANI and liberate more infiltrated water

molecules, leading to a significant increase in the resistance

of PANI [49, 50]. As shown in Fig. 7c, the ethanol

response increases with increasing humidity, even in high

humidity levels. These results reveal that the device has

potential application under high humidity levels in gas

flow, such as in the case of human breath analysis.

The working mechanism of the self-powered exhaled

breath analyzer is simply shown in Fig. 8. The schematic

diagram of the induced piezoelectric effect of PVDF is

shown in Fig. 8a. Under blowing-induced deformation, the

polarized dipoles in PVDF become parallel-aligned to

create surface charge separation. According to the funda-

mental piezoelectric theory, the generated open-circuit

voltage (VOC) and short-circuit current (ISC) of piezoelec-

tric PVDF can be written as [33]:

VOC ¼ g33rYd; ð2ÞISC ¼ d33YAe; ð3Þ

where g33 is the piezoelectric voltage constant, d33 is the

piezoelectric coefficient, Y is Young’s modulus, r is the

strain in perpendicular direction, d is the thickness, A is the

effective cross-sectional area, and e is the applied strain.

When the device is under gas flow, a current can be

measured in the external circuit (Fig. 8b). While the

blowing maintains a constant gas flow rate, the generated

piezoelectricity of PVDF will be stable, and the resistance

of PANI electrodes can be significantly influenced by gas

species and concentration in the gas flow [39], giving rise

to the variation of measured output current in the external

circuit (Fig. 8c). To prove this mechanism, the I–V curve of

the PANI(SDS) sensing unit is measured under 0, 300, and

In ethanolIn air

80

60

40

20

0

Cur

rent

(nA

)

40 60 80 100Relative humidity (RH, %)

80

60

40

20

0

Res

pons

e (%

)

40 60 80 100Relative humidity (RH, %)

(b)

(a)

(c)

80

40

0

− 40

− 80

Cur

rent

(nA

)

40% RH 60% RH 80% RH 100% RH

Air AirEthanol Ethanol Air AirEthanol Ethanol

0 5 10Time (s)

15 20

Fig. 7 Humidity influence on ethanol response in the PANI(SDS) sensing unit. a The output current of the PANI(SDS) sensing unit under

airflow and 600 ppm ethanol gas flow in different humidity conditions (40%, 60%, 80%, and 100% RH). b The relationship between output

current and relative humidity in airflow and 600 ppm ethanol gas flow. c The relationship between response and relative humidity

Original

)c()b()a(

Cu PANI PVDF Gas moleculeDeformed in gas markerDeformed in air

V+

V−

AAA

Fig. 8 Working principle of the device. a The original state of polarized PVDF. b Measuring the output current in air atmosphere. c Measuring

the output current in gas marker atmosphere

123

Nano-Micro Lett. (2018) 10:76 Page 9 of 12 76

600 ppm ethanol gas flow, shown in Fig. S5, and demon-

strates the same response compared with self-powered gas-

sensing performances. The interaction between gas mole-

cules and PANI is multiform: For small molecules (CO and

CH4), the increased resistance can be attributed to chain

expansion induced by interposition of gas molecules into

PANI [51–53]; for acetone and ethanol, weak chemical

interactions between gas molecules and PANI dominate the

decrease in doping level, leading to the increased resistance

[54, 55]; and for NOx, a well-known oxidizing gas, PANI

will be oxidized and positively charged by transferring

electrons to NOx molecules, resulting in the decreased

resistance of PANI and increase in output current [56].

When the atmosphere returns to air, adsorbed gas mole-

cules are removed from PANI chains, and thus measured

current in the external circuit recovers to its original value.

Figure S6 shows the SEM image of PANI(NA) upon

exposure to CH4, indicating that the surface morphology is

significantly influenced by interposed gas molecules. Fig-

ure S7 shows the thickness of PANI(NA) before and after

exposure to NH4, showing that the thickness is slightly

affected by gas adsorption as well.

The blowing-driven PANI/PVDF bellows as an exhaled

breath analyzer is demonstrated to detect ethanol in

exhaled gas, as shown in Fig. 9. As ethanol gas presents

itself in the exhaled breath of fatter liver patient, a healthy

adult can mimic a fatty liver patient after drinking a certain

amount of beer (Fig. 9a). The blowing is sustained for 5 s,

and the highest gas flow rate is * 3 m s-1. The output

current of the PANI(SDS) sensing unit is measured to

represent ethanol concentration. As the adult blows into the

self-powered analyzer prior to drinking beer (Fig. 9b), the

output current is 8–12 nA. (The blowing rate is not con-

stant.) As the adult blows into the self-powered analyzer

after drinking one and two cups of beer, the output current

drops from 10 to 7 nA (Fig. 9c) and from 10 to 5 nA

(Fig. 9d), respectively. These results demonstrate that the

PANI/PVDF piezo-gas-sensing arrays can be used as

breath analyzer for a potential diagnostics application. It is

worth noticing that although the sensor arrays can selec-

tively detect several gas markers, the sensitivity and

detection limit are insufficient for practical use in the

current case. In the future, more work needs to be done to

detect ppb-level gas markers, which will involve con-

structing composites of PANI derivatives and metal oxide

nanostructures [57, 58].

4 Conclusions

In summary, a blowing-driven bellows based on a PANI/

PVDF piezo-gas-sensing array has been presented as non-

invasive and self-powered exhaled breath analyzer for

potential diagnostic applications. The device works by

converting energy from blowing of exhaled breath into

electrical sensing signals without any external power

sources. Five sensing units in a single device can be used

for diagnosis of liver cirrhosis, airway inflammation,

15

10

5

0

− 5

− 10

− 15

Cur

rent

(nA

)

0 1 2Time (s)

3 4 5 6

Blowing without drinking

(b)

15

10

5

0

− 5

− 10

− 15

Cur

rent

(nA

)

0 1 2Time (s)

3 4 5 6

(d)15

10

5

0

− 5

− 10

− 15

Cur

rent

(nA

)

0 1 2Time (s)

3 4 5 6

reeb fo spuc 2 gniknird retfAreeb fo puc 1 gniknird retfA

(c)

(a)

Fig. 9 Demonstration of self-powered PANI/PVDF breath analyzer. a Photograph of the measurement platform. b–d The output current of the

device in response to blowing by an adult. b Without drinking, c after drinking one cup of beer, and d after drinking two cups of beer

123

76 Page 10 of 12 Nano-Micro Lett. (2018) 10:76

diabetes, and asthma by detecting the gas markers in

exhaled breath at concentrations in the range from 0 to

600 ppm. The sensing units exhibit excellent room-tem-

perature response/recovery kinetics, and the response is

maintained constant under different gas flow rates. The

working principle can be attributed to the coupling of in-

pipe gas-flow-induced piezoelectric effect of PVDF and

gas-sensing properties of PANI electrodes. In addition, the

device is demonstrated for detecting ethanol concentration

in exhaled breath. This work launches a new working

principle in the exhaled breath detection field and greatly

advances the applicability of self-powered systems.

Acknowledgements This work was supported by the National Nat-

ural Science Foundation of China (11674048), the Fundamental

Research Funds for the Central Universities (N170505001 and

N160502002), and Program for Shenyang Youth Science and Tech-

nology Innovation Talents (RC170269).

Open Access This article is distributed under the terms of the

Creative Commons Attribution 4.0 International License (http://crea

tivecommons.org/licenses/by/4.0/), which permits unrestricted use,

distribution, and reproduction in any medium, provided you give

appropriate credit to the original author(s) and the source, provide a

link to the Creative Commons license, and indicate if changes were

made.

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